Preparation method of chalcopyrite-type compounds with microwave irradiation

ABSTRACT

A method for preparing a chalcopyrite-type semiconductor compound which is widely used as a sunlight-absorbing material. More specifically, disclosed is a method for preparing a chalcopyrite-type compound, in which microwaves are used as heat sources in the preparation of the chalcopyrite-type compound, and the chalcopyrite-type compound can be produced in a large amount in a short reaction time using a batch or continuous reactor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing fromInternational Application No. PCT/KR2008/001762 filed Mar. 28, 2008,which claims priority to Korean Application No. 10-2007-0108908 filedOct. 29, 2007 and to Korean Application No. 10-2007-0097697 filed Sep.28, 2007, the teachings of all of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a method for preparing achalcopyrite-type compound, which is commonly used as asunlight-absorbing material or the like.

BACKGROUND OF THE INVENTION

CuInSe₂ (CIS), which is a typical chalcopyrite, has a very high solarcell efficiency up to 17% and has generally been prepared through highvacuum process fabricating thin films, including selenization processes,which comprise vacuum deposition, the decomposition and deposition oforganometallic compounds, electrochemical deposition or sputtering, orsolid phase reactions, which requires a high synthetic temperaturehigher than 600° C. (U.S. Pat. Nos. 5,356,839 and 5,045,409; Thin SolidFilms 1994, 245,174, Chem. Mater. 2003, 15, 3142). However, thesemethods have problems which includes expensive equipment and high energycosts.

Carmalt et al. could obtain CuInSe₂ at a relatively low temperatureafter carrying out a reflux reaction for 72 hours. However, in thismethod the heat treatment at a temperature higher than 500° C. mustnecessarily be carried out in order to obtain crystalline CuInSe₂ (J.Mater. Chem. 1998, 8 2209).

Li, Yang, Chun et al. reported that CIS particles were synthesized atlow temperature through a solvothermal method from copper dichloride(CuCl₂), indium trichloride (InCl₃) and selenium (Se) powders as rawmaterials using an amine compound as a solvent or a chelating agent(Adv. Mater. 1999, 11, 1456, J. Phy. Chem. 2006, 110, 17370; KoreanPatent Laid-Open Publication No. 10-2005-0037495). However, this methodneeds long reaction time (more than 12 hours) and the CuSe and Sepowders remain in trace amounts.

A reflux reaction method that uses microwaves as a heat source in thesolvothermal synthesis of CIS was reported (Inorg. Chem. 2003, 42,7148). In this method, even though the reaction is completed within ashort synthesis time (1 hour), CuSe-associated impurities remain and thecrystallinity of the product is relatively low, and there is alimitation in carrying out a continuous preparation process commerciallyproducing CIS. In addition, even though polyol, used as a reactionsolvent in this method, it is generally used as a reducing agent and itcan cause oxidation of CIS, because it contains oxygen in the molecule.

Thus, there is a general need for a method of preparingchalcopyrite-type compound that avoids or solves one or more of theabove-mentioned problem of prior art methods. There is particular needfor a method of preparing chalcopyrite-type compounds having highcrystallinity and/or little or no impurities. For purposes of processefficiencies, there is also need for a method of preparingchalcopyrite-type compound having a short reaction time and little to nounreacted materials

SUMMARY OF THE INVENTION

In an embodiment of the present invention is provided a method forpreparing a chalcopyrite-type compound. The compound may have highcrystallinity and little or no impurities.

In another embodiment of the invention, a method is provided forpreparing a pure chalcopyrite-type compound comprising Cu, a group IIIelement and a group VI element, in which the solubility of reactants(including a Cu salt, a group III element salt and a group VI elementpowder), is increased during the preparation of the chalcopyrite-typecompound, so that the chalcopyrite-type compound contains no unreactedmaterials or oxides.

In a further embodiment of the present invention is provided a methodfor preparing a chalcopyrite-type compound, in which no unreactedmaterials remain and the reaction time is short, and thus thechalcopyrite-type compound can be efficiently produced at high purity ina large amount.

In still a further embodiment of the invention, a method for preparing achalcopyrite-type compound represented by the following Formula 1,CuM¹M² ₂, is provided. The method of this embodiment comprises mixing aCu salt, a group III element salt and a group VI element powder with achelating agent, an ionic liquid or a chelating agent-ionic liquidmixture and then heating the mixture solution by microwave irradiation.With reference to the formula, CuM¹M² ₂, M¹ is at least one selectedfrom among the group III elements, and M² is at least one selected fromamong the group VI elements. The mixture may be formed in a reactor andthen irradiated.

Chalcopyrite-type compound, prepared by some embodiments of thepreparation method of the present invention, has advantages in that,when the prepared compound is analyzed by XRD, no impurities aredetected in the compound, and in addition, the prepared compound hashigh crystallinity and uniform particle size.

DESCRIPTION OF DRAWINGS

The following drawings are illustrative of particular embodiments of thepresent invention and therefore do not limit the scope of the invention.The drawings are not to scale (unless so stated) and are intended foruse in conjunction with the explanations in the following detaileddescription. Embodiments of the present invention will hereinafter bedescribed in conjunction with the appended drawings, wherein likenumerals denote like elements.

FIG. 1 is the X-ray diffraction pattern of CuInSe₂ prepared in Example 1of the present invention;

FIG. 2 is the X-ray diffraction pattern of CuInSe₂ prepared in Example 2of the present invention;

FIG. 3 is the X-ray diffraction pattern of CuIn_(0.5)Ga_(0.5)Se₂prepared in Example 3 of the present invention;

FIG. 4 shows the construction of a microwave reactor system comprisingcontinuous tubular reactors; and

FIG. 5 shows the construction of a microwave reactor system comprising acontinuous stirred-tube reactor.

The following is a list of reference numerals identifying the componentto which they refer: 10: reactant drum; 11: slurry feed pump; 20:preheater; 21: pressure indicator; 22: temperature indicator; 30:tubular reactors; 31: microwave ovens; 32: microwaves; 33: temperatureindicator and controller; 34: rupture; 37: microwave barrier; 38: sightglass; 39: magnetron; 40: cooler; 41: product drum; 42: pressureindicator and controller; 43: outlet; 44: nitrogen; 45: drain line; and50: continuous stirred-tank reactor.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is notintended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the following description provides somepractical illustrations for implementing exemplary embodiments of thepresent invention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements, and allother elements employ that which is known to those of ordinary skill inthe field of the invention. Those skilled in the art will recognize thatmany of the noted examples have a variety of suitable alternatives.

The inventors have made many efforts to solve some of theabove-described short comings occurring in the prior art. The inventorshave found that with methods according to some embodiments of theirinvention, they have been able to remarkably increase the solubilitiesof reactants, including group VI element powder, by introducing amixture of a Cu salt, a group III element salt, a group VI elementpowder and a chelating agent into a closed, high-pressure reactor, andthen heating the introduced mixture by microwave irradiation. Further,according to some embodiments of the method of the invention, theinventors were able to prepare a pure chalcopyrite-type compoundcontaining no unreacted materials, even though the reaction time wasshorter than 1 hour.

In an embodiment of method of the invention for preparing achalcopyrite-type compound represented by the following Formula 1, themethod comprising the steps of a) mixing a Cu salt, a group III elementsalt and group VI element powder with a chelating agent, an ionic liquidor a chelating agent-ionic liquid mixture; and b) introducing themixture solution into a reactor and heating the introduced mixturesolution by microwave irradiation.

CuM¹M² ₂  [Formula 1]

wherein M¹ is at least one selected from among the group III elements,and M² is at least one selected from among the group VI elements.

In the formula 1, M¹ is selected from among Ga, In, Tl and mixturesthereof, and M² is selected from among S, Se, Te and mixtures thereof.

The Cu salt and the group III element salt are not specifically limited,as long as they can be dissolved in a solvent. Halides or hydratesthereof may be used.

The chelating agent may be one or a mixture of two or more selectedamong the bidentate ligands having a coordination number of 2, andtridentate ligands having a coordination number of 3. The chelatingagent serves to stabilize the reactants using the coordinate covalentbond of metal elements and reduce the reaction rate, such that a uniformreaction can occur. Also, it serves as a solvent. It is preferable touse an amine compound having the following formula 2 to help control thereaction rate:

wherein R is a straight or branched-chain C₂-C₈ alkylene and may besubstituted with an amino group (—NH₂), and the carbon atom of R may besubstituted with a nitrogen atom.

The amine compound may be selected among ethylenediamine,1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine,1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine anddiethylenetriamine ((NH₂CH₂CH₂)₂NH).

The ionic liquid may be used as a solvent in the present invention,because it has high solvent power and selectively absorbs microwaves. Itis thought that the constituting elements of a compound forming theionic liquid enhances the ionic character for Cu²⁺ and InSe₂ ⁻, whichare the counter ions of the chalcopyrite compound, so as to reduce thecontact frequency between the ions of the chalcopyrite compound, thusserving as a chelating agent, such as amine.

Generally, the ionic liquid is a salt, which melts at a relatively lowtemperature and has non-molecular ionic properties. It remains as aliquid at a relatively low temperature, i.e., temperature ranging fromroom temperature to 200° C., and has a relatively low viscosity, evenwhen it melts. The ionic liquid may be at least one selected amongimidazolium, pyrazolium, triazolium, thiazolium, oxazolium,pyridazinium, pyrimidinium, pyrazinium, ammonium, phosphonium,sulfonium, pyridinium and pyrrolidinium salts, which are non-substitutedor substituted with an alkyl group having 1-15 carbon atoms. The anionof the ionic liquid forming the salt is not specifically limited, andexamples thereof include halides (F⁻, C⁻, Br⁻ and I⁻), acetate(CH₃COO⁻), trifluoroacetate (CF₃COO⁻), triflate (CF₃SO₃ ⁻), sulfate (SO₄²⁻), hydrogen sulfate (HS0₄ ⁻), methyl sulfate (CH₃0SO₃ ⁻), ethylsulfate (C₂H₅OSO₃ ⁻), sulfite (SO₃ ²⁻), hydrogen sulfite (HSO₃ ⁻),chloroaluminates (AlCl₄ ⁻, Al₂Cl₇ ⁻ and Al₃Cl₁₀ ⁻), tetrabromoaluminate(AlBr₄ ⁻), nitrite (NO₂ ⁻), nitrate (NO₃ ⁻), dichlorocuprate (CuCl₂ ⁻),phosphate (PO₄ ³⁻), hydrogen phosphate (HPO₄ ²⁻), dihydrogen phosphate(H₂PO₄ ⁻), carbonate (CO₃ ²⁻), hydrogen carbonate (HCO₃ ⁻), sulfonate(SO₃ ⁻), tosylate (p-CH₃C₆H₄SO₃ ⁻) and bis(trifluoromethylsulfonyl)imide((CF₃S0₂)₂N⁻).

An alcoholic solvent may further be added to the mixture. The use of thealcoholic solvent has advantages in that it can control the rate of themicrowave reaction and control the shape of the preparedchalcopyrite-type compound. The alcoholic solvent may be a monoalcoholhaving one hydroxyl group, a diol compound having two hydroxyl groups,or a mixture thereof. Examples of the monoalcohol may include ethanol,methanol, isopropanol and the like, and examples of the diol compoundmay include ethylene glycol, 1,3-propanediol, 1,2-propanediol,1,4-butanediol, 1,2-hexanediol, 1,3-hexanediol, 2-ethyl-1,3-hexanediol,3-chloro-1,2-propanediol, 1-buten-1,4-diol, 1,2-octanediol,7-octen-1,2-diol, 1,2-cyclohexanediol, 1,3-cyclohexanediol,1,2-cyclopentanediol, 1,3-cyclopentanediol and the like.

In the step b), it is preferable to introduce the mixture into thereactor after removing oxygen from the reactor, so that the productionof impurities by reaction with oxygen can be suppressed. The method ofremoving oxygen from the reactor may be, for example, a method ofpurging the reactor with inert gas, such as nitrogen, helium or argon,or a method of repeatedly purging and pumping the inert gas into thereactor.

The microwaves which are used as a heat source in the high-temperaturereaction of preparing the chalcopyrite-type compound in the presentinvention, are any microwaves having a frequency of 500 MHz-30 GHz canbe used to heat the reactants, but it is convenient and efficient to usemicrowaves having a frequency of 2.54 GHz, which are commonly used inindustrial applications. In addition, in high-power systems for massproduction, microwaves having a frequency of 915 MHz may also be used.

Although the reaction temperature in the preparation method according tothe present invention is not specifically limited to the temperaturebetween 100° C. and 250° C., and more preferably between 120° C. and220° C. If the reaction temperature is excessively low, it is noteffective, because the reaction rate is slow. On the other hand, if thereaction temperature is excessively high, the reaction rate isexcessively fast, and thus there is a greater probability thatimpurities other than CIS will be produced. In this case, the internalpressure in the reactor is increased, and thus the construction of thereactor is not economical. Although the pressure of the reactor is notspecifically limited, the synthetic process is preferably carried out atthe autogeneous pressure of the reactants at the reaction temperature.Also, for the elimination of oxygen in the reactor and for a continuousreaction, inert gas, such as nitrogen or helium, may be added to thereactor, in which case the reaction may be carried out at hightemperature. The pressure of the reactor during the reaction ispreferably set within 2-30 atm. If the pressure is less than 2 atm, itis disadvantageous in that the crystallinity of the reactants isreduced, and if the pressure exceeds 30 atm, there is a disadvantage inthat the stability of the whole system is difficult to maintain.

The reaction in the step b) may be carried out in a batch or continuousmanner using a closed, high-pressure reactor. The batch reactor issuitable for producing a small amount of CIS, because it has low hourlyproductivity, and the continuous reactor incurs a high investment cost,but is suitable for mass production. The reaction time is preferablyabout 1 minute to 3 hours for a batch reaction. If the reaction time isexcessively long, impurities tend to be incorporated, and if thereaction time is excessively short, the rate of formation of reactioncrystals is very low. The reaction time more preferably ranges from 1minute to 1 hour. The residence time in the continuous reactorpreferably ranges from about 1 minute to 1 hour. If the residence timeis excessively long, productivity is low and large particles areobtained, and if the residence time is excessively short, the reactionconversion rate is low. The residence time is more preferably 1-20minutes. The reactants may also be stirred during the batch orcontinuous reaction, and the stirring speed is preferably 100-1000 rpm.

When the step b) is carried out using a continuous microwave, reactor,it may comprise the steps of: feeding a mixture, obtained by a Cu salt,a group III element salt and a group VI element powder with a chelatingagent, either into two or more continuous tubular reactors, or into acontinuous stirred-tank reactor; heating the mixture in the tubularreactors or the continuous stirred-tank reactor using microwaves tocontinuously prepare a chalcopyrite-type compound; and separating asolid and a liquid from the prepared reaction product, and thenmeasuring the remaining gas to control the pressure in the reactor.

An example of the continuous microwave reactor used in the presentinvention is shown in FIG. 4. which comprises of a continuous tubularreactor, is disclosed in Korean Patent Registration No. 0693126, filedin the name of the present inventors. The continuous microwave reactorsystem comprises a reactant drum 10 for stirring and storing reactants,a slurry pump 11 for transporting the reactant slurry of the reactantdrum, a preheater 20, tubular reactors 30, a temperature indicator andcontroller 33, a cooler 40, a product drum 41 for storing a product, anda pressure indicator and controller 42. In the reactant drum 10, the rawmaterials can be metered and stirred, and the reactants can becontinuously supplied using the slurry pump 11. The supplied reactantscan be preheated to the maximum reaction temperature in the preheater 20using microwaves or an electric heater. The tubular reactors 30 are madeof a material that is permeable to microwaves, such as Teflon or aceramic material, and is preferably made of Teflon, in view ofprocessability. The tubular reactors 30 can be connected with each otherin series in order to increase the residence time, and can be connectedin parallel in order to increase productivity. In FIG. 4, two tubularreactors 30 are connected in series, and home microwave ovens 31 areshown as sources providing microwaves 32 to the tubular reactors. Whenhome microwave ovens are used, the microwaves 32 are relativelyuniformly distributed in the ovens, and thus microwaves can be evenlyirradiated into the tubular reactors. After the completion of thereaction, the product is cooled, the solid and the liquid are collectedin the product drum 41, and the gas is vented through thepressure-controlling unit 42. In the case of larger scale production, itis more effective to place a separation tank (not shown) capable ofperforming solid-liquid separation, in place of the production drum 41,and provide processes, including liquid removal, drying and packaging.In the pressure controlling unit, the pressure of gas can be accuratelymeasured without the interference of a liquid or a solid. This pressureindicates the pressure in the reactor, and thus the pressure in thereactor can be very stably controlled.

The residence time in one reactor is preferably about 1 minute to 1hour. If the residence time is excessively long, productivity will below, and if the residence time is excessively short, the reactionconversion rate will be low. The residence time in each reactor is morepreferably 1 minute to 20 minutes.

The tubular reactors preferably have no connection in a region which isirradiated with microwaves, and the length of the tubular reactors ispreferably 5-100 cm per magnetron (microwave generator). If the lengthis excessively short, an increased number of reactors is required,leading to inefficiency, and if the length is excessively long,differential pressure tends to form, and the construction of thereactors is inefficient. Two or more tubular reactors can be connectedin series or in parallel, and the number of connected tubular reactorsis not specifically limited, but is preferably 2-10 minutes in view ofefficiency. Because the microwave reaction occurs rapidly, it ispreferable to sufficiently stir the reactants before the reaction, andit is particularly preferable to preheat the reactants to a temperaturebetween room temperature and the reaction temperature.

Another example of the continuous microwave reactor used in the presentinvention is shown in FIG. 5. The microwave reactor system comprising acontinuous stirred-tank reactor (CSTR) 50, is disclosed in Korean PatentRegistration No. 0627634, filed in the name of the present inventors. Inthe reactor drum 10 in FIG. 5, the raw materials can be placed andstirred, and the reactants in the reaction drum 10 can be continuouslysupplied into the continuous stirred-tank reactor 50 using the slurrypump 11. The continuous stirred-tank reactor 50 is made of stainlesssteel, titanium or hastelloy, or other corrosion resistant metal ormetal alloy and is preferably made of stainless steel. In order toirradiate microwaves, a thick sight glass 38, made of a glass, quartz orceramic material, all of which are permeable to microwaves, is placed inthe wall of the continuous stirred-tank reactor 50. With an increase inthe capacity of the reactor, the number of sight glasses and the numberof magnetrons 39 for producing microwaves can be increased. A microwavebarrier 37, such as stainless steel mesh can be installed to preventmicrowaves from leaking to the outside of the reactor. A drain line 45is connected to the side of the continuous stirred-tank reactor 50 at alocation having a given height, such that a liquid and a solid areautomatically drained, when the level of the reactor increases above aset value. The gas component is passed through a cooler 40, disposedabove the reactor, to the pressure indicator and controller 42, and isautomatically vented from outlet 43 when the pressure of the reactor isabove a set pressure value. A plurality of the continuous stirred-tankreactors 50 may be connected in series in order to increase theresidence time or to reduce unreacted components due to the widedistribution of residence times. When pluralities of the reactors areconnected with each other, it is preferable to allow the reactants toflow downward.

As described above, the preparation method according to the presentinvention is a very economical method capable of synthesizing achalcopyrite-type compound in a very short time using microwaveirradiation. This method can also produce large amounts of achalcopyrite-type (Cu-III-VI₂) semiconductor compound in a very shorttime of less than 5 minutes.

Also, the chalcopyrite-type compound prepared according to the inventivemethod has advantages in that it has very high purity compared to thatof a product prepared according to prior art preparation methods,because the reactant group VI element powder does not remain andbyproducts caused by oxygen are not produced, and in that it has highcrystallinity and a uniform particle size. Moreover, when the continuousmicrowave synthetic technology is used, there is an advantage in thatthe concentration of the product can be increased two-fold or morecompared to that in a prior electrical heating method using asolvothermal synthetic process, leading to a significant increase inhourly productivity. In addition, when microwave irradiation isperformed, there is an advantage in that pure CIS can be synthesized,because the solubility of Se powder in an amine compound is very high.

Hereinafter, the present invention will be described in further detailwith reference to examples. It is to be understood, however, that theseexamples are illustrative only, and the scope of the present inventionis not limited thereto.

Example 1

4 g (29.75 mmol) of copper dichloride (CuCl₂), 8.8 g (30.01 mmol) ofindium trichloride (InCl₃ 4H₂O) and 4.74 g (60.03 mmol) of seleniumpowder were added to 500 ml of a mixed solution of ethylenediamine (ED):ethanol (E) (ED:E=3:1 molar ratio). The mixture was introduced into amicrowave reactor (CEM, Model Mars-5), from which oxygen has beenremoved by purging with nitrogen under a nitrogen stream, and wasirradiated with microwaves having a frequency of 2.54 GHz to elevate thereaction temperature to 140° C., and the mixture was maintained atautogeneous pressure (about 4 atm) for 5 minutes, so that the mixture inthe reactor was allowed to react. Then, the reaction product was cooledto room temperature, centrifuged, washed with ethanol and distilledwater, and dried in a nitrogen atmosphere at 80° C., thus preparing achalcopyrite CuInSe₂ compound. The X-ray diffraction pattern of thesynthesized powder was analyzed (Rigaku Japan, D/max-A, CuK:=1.54178 Å)and, consistent with JCPDS No. 89-5647 (FIG. 1).

As shown in FIG. 1, unreacted Se powder and other impurities were notdetected in the CuInSe₂ compound in this Example, and the preparedcompound had high crystallinity.

Example 2

4 g (29.75 mmol) of copper dichloride (CuCl₂), 8.8 g (30.01 mmol) ofindium trichloride (InCl₃4H₂O) and 4.74 g (60.03 mmol) of seleniumpowder were added to 500 ml of ethylenediamine (ED). The mixture wasintroduced into a microwave reactor (CEM, Model Mars-5), from whichoxygen has been removed by purging with nitrogen, under a nitrogenstream, and was irradiated with microwaves having a frequency of 2.54GHz to elevate the reaction temperature to 180° C., and the mixture wasmaintained at autogeneous pressure (about 3.5 atm) for 30 minutes, sothat the mixture in the reactor was allowed to react. Then, the reactionproduct was cooled to room temperature, centrifuged, washed with ethanoland distilled water, and dried in a nitrogen atmosphere at 80° C., thuspreparing a chalcopyrite CuInSe₂ compound. The X-ray diffraction patternof the synthesized powder was analyzed (Rigaku Japan, D/max-A,CuK:=1.54178 Å) and it was found to be consistent with JCPDS No. 89-5647(FIG. 2).

As shown in FIG. 2, it could be seen that the CuInSe₂ compound preparedin this Example was a nanocrystal having a particle size of 28 nm, ascalculated from the full width half max of the XRD peak.

Example 3

4 g (29.75 mmol) of copper dichloride (CuCl₂), 4.398 g (15.00 mmol) ofindium trichloride (InCl₃4H₂O), 1.046 g (15.00 mmol) of Ga and 4.74 g(60.03 mmol) of selenium powder were added to 500 ml of ethylenediamine(ED): ethanol (E) (ED:E=3:1 molar ratio). The mixture was introducedinto a microwave reactor (CEM, Model Mars-5), from which oxygen has beenremoved by purging with nitrogen, under a nitrogen stream, and wasirradiated with microwaves having a frequency of 2.54 GHz to elevate thereaction temperature to 180° C., and the mixture was maintained atautogeneous pressure (about 4 atm) for 5 minutes, so that the mixture inthe reactor was allowed to react. Then, the reaction product was cooledto room temperature, centrifuged, washed with ethanol and distilledwater, and dried in a nitrogen atmosphere at 80° C., thus preparing achalcopyrite CuIn_(0.5)Ga_(0.5)Se₂ compound. The X-ray diffractionpattern of the synthesized powder was analyzed (Rigaku Japan, D/max-A,CuK:=1.54178 Å) and it was consistent with JCPDS No. 89-5647 (FIG. 3).This result suggests that the metal powders are synthesized in arelatively short time in the microwave irradiation process compared to aconventional electrical heating process.

Example 4

A chalcopyrite compound was synthesized in the same manner as in Example2, except that an ionic liquid, 1-butylimidazolium chloride, was usedinstead of ethylenediamine (ED) as the solvent. The X-ray diffractionpattern of the synthesized powder was analyzed (Rigaku Japan, D/max-A,CuK:=1.54178 Å) and, as a result, it was consistent with JCPDS No.89-5647.

Example 5 Continuous Microwave Reactor System

As a system for preparing a chalcopyrite compound, the continuousmicrowave reactor shown in FIG. 4 was used. In the reactant drum 10, thereactants were be metered to make a reactant mixture, and the slurrypump 11 was used to transfer the reactant mixture to the preheater 20,the microwave reactor 30, the cooler 40 and the product drum 41. In aportion of the reactor, into which microwaves were not irradiated, apressure gauge 21 and a thermocouple 22 were placed, such that thetemperature and pressure of the reactant or the product could bemeasured. The reaction temperature could be controlled by controllingthe power of microwaves, and a rupture 34 was provided, such that, whena rapid increase in pressure occurred, gas could be automatically ventedfrom the reactor, thus preventing the internal pressure of the reactorfrom excessively increasing and an explosion from occurring in thereactor. The obtained product could be collected in the product drum 41,the pressure of the reactor was controlled by measuring the pressure ofthe gas component remaining after the removal of the solid and liquidcomponents of the product, and, when the pressure in the reactor washigher than a set pressure value, gas was discharged outside through thepressure controller 42. In order to perform the reaction in a smooth andstable manner and to prevent the evaporation of the solvent, it ispreferable to maintain the reactor pressure at a set pressure valuebefore the start of the reaction, and for this purpose, a nitrogen tank44 for supplying nitrogen was used. In order to prevent microwaves fromleaking from the reactor, a stainless steel mesh was disposed around thereactor.

Preparation of CuInSe₂ Compound

4 g (29.75 mmol) of copper dichloride (CuCl₂) 8.8 g (30.01 mmol) ofindium trichloride (InCl₃4H₂O), and 4.74 g (60.03 mmol) of selenium (Se)powder were added to 500 ml of ethylenediamine (ED) to prepare a mixturesolution. The continuous microwave reactor system was purged withnitrogen to form a nitrogen atmosphere, and in this state, nitrogen wassupplied into the microwave reactor 30 to maintain the reactor pressureat 15 atm. Then, the mixture solution was pumped, so that it wascontinuously supplied from the reactant drum 10 to the microwave reactor30. The mixture in the reactor was irradiated with microwaves having afrequency of 2.54 GHz to increase the reactor temperature to 180° C.,and when the reactor temperature exceeded 4 atm, gas was vented from thereactor so as to maintain the reactor pressure to 4 atm. The residencetime in each of the reactors was 5 minutes, and from 5 minutes after theinitiation of the reaction, the product was collected in the productdrum 41. The product was cooled to room temperature, centrifuged, washedwith ethanol and distilled water, and dried in a nitrogen atmosphere at80° C., thus preparing a chalcopyrite CuInSe₂ compound. The X-raydiffraction pattern of the synthesized powder was analyzed (RigakuJapan, D/max-A, CuK:=1.54178 Å), and, as a result, it was found to beconsistent with JCPDS No. 89-5647. Ethylenediamine has advantages inthat it can completely dissolve powder such as Se, and thus isadvantageous for carrying out a continuous reaction.

Thus, embodiments of the invention are disclosed. Although the presentinvention has been described in considerable detail with reference tocertain disclosed embodiments, the disclosed embodiments are presentedfor purposes of illustration and not limitation and other embodiments ofthe invention are possible. One skilled in the art will appreciate thatvarious changes, adaptations, and modifications may be made withoutdeparting from the spirit of the invention and the scope of thedisclosure.

1. A method for preparing a chalcopyrite-type compound represented bythe following formula 1, and the method comprising the steps of: a)mixing a Cu salt, a group III element salt and a group VI element powderwith a chelating agent, an ionic liquid or a chelating agent/ionicliquid mixture to prepare a mixture solution; and b) introducing themixture solution into a reactor and heating the introduced mixturesolution by microwave irradiation:CuM¹M² ₂  [Formula 1] wherein M¹ is one or more selected from amonggroup III elements, and M² is one or more selected from among group VIelements.
 2. The method of claim 1, wherein M¹ is selected among Ga, In,Tl and mixtures thereof, and M² is selected among S, Se, Te and mixturesthereof.
 3. The method of claim 1, wherein the chelating agent isselected from among amine compounds, represented by the followingFormula 2, and mixtures thereof:

wherein R is a straight or branched-chain C₂-C₈ alkylene, which may besubstituted with an amino group (—NH₂), and the carbon atom of R may besubstituted with a nitrogen atom.
 4. The method of claim 3, wherein theamine compound is selected among ethylenediamine, 1,3-propanediamine,1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine,1,7-heptanediamine, 1,8-octanediamine and diethylenetriamine.
 5. Themethod of claim 1, wherein the ionic liquid is one or more selectedamong imidazolium, pyrazolium, triazolium, thiazolium, oxazolium,pyridazinium, pyrimidinium, pyrazinium, ammonium, phosphonium,sulfonium, pyridinium and pyrrolidinium salts, which are non-substitutedor substituted with an alkyl group having 1-15 carbon atoms.
 6. Themethod of claim 1, wherein an alcoholic solvent is further added to themixture solution.
 7. The method of claim 6, wherein the alcoholicsolvent is selected among monoalcohols, including ethanol, methanol andisopropanol, diol compounds, including ethylene glycol, 1,3-propanediol,1,2-propanediol, 1,4-butanediol, 1,2-hexanediol, 1,3-hexanediol,2-ethyl-1,3-hexanediol, 3-chloro-1,2-propanediol, 1-buten-1,4-diol,1,2-octanediol, 7-octen-1,2-diol, 1,2-cyclohexanediol,1,3-cyclohexanediol, 1,2-cyclopentanediol and 1,3-cyclopentanediol, andmixtures thereof.
 8. The method of claim 1, wherein the mixture solutionin the step (b) is introduced into the reactor under an inert gasstream, after oxygen in the reactor is removed.
 9. The method of claim1, wherein the reactor is a batch or continuous, closed, high-pressurereactor.
 10. The method of claim 9, wherein the microwaves in the step(b) are irradiated such that the reaction temperature reaches 100-250°C.
 11. The method of claim 10, wherein the pressure of the reactorduring the reaction in the step (b) is controlled to 2-30 atm.
 12. Themethod of claim 10, wherein the microwaves in the step b) have afrequency of 500 MHz-30 GHz.
 13. The method of claim 10, wherein thereaction time in the step b) ranges from 1 minute to 1 hour.
 14. Themethod of claim 1, wherein, in the step b), the chalcopyrite-typecompound is continuously prepared using tubular reactors or a continuousstirred-tank reactor.